The subject matter of the present invention is new organosilane esters which give improved effectiveness to sealing compositions. The improved effectiveness manifests itself especially in the case of sealing compositions on a polyurethane basis, whose adhesivity and elongation are improved considerably by the addition of these new silanes.
Organosilane esters are known, whose organofunctional groups have a substituted or unsubstituted amino, mercapto or glycidyl moiety, and which contain, as silicon-functional ester groupings, alkoxy moieties whose alkyl grouping is not interrupted by oxygen atoms. Examples of these known organofunctional silane esters are gamma-aminopropyltriethoxysilane, N-beta-aminoethyl-gamma-aminopropyltrimethoxysilane, gamma-mercaptopropyltrimethoxysilane or gamma-glycidyloxypropyltrimethoxysilane.
These known organosilane esters are known to increase adhesion between various polymers and inorganic, oxidic or metallic substrates, such as glass, concrete or aluminum, for example. On the basis of these adhesion-improving properties it has already been proposed to use these silane esters in polyurethane sealing compositions. When these known organosilane esters are used in polyurethane sealing compositions, however, it has been found disadvantageous that their effect does not fully develop until a relatively long time after they have been incorporated. The problem therefore existed of finding organofunctional silane esters which develop their full effectiveness, especially in polyurethane sealing compositions, as soon as possible after they have been incorporated.
As a solution to this problem, organosilane esters have been discovered having the formula: EQU Y--(CH.sub.2).sub.n --Si(CH.sub.3).sub.m X.sub.p Z.sub.3-(m+p),
wherein
Y represents a moiety from group NHR (R=H or C.sub.1-6 alkyl or phenyl or --(CH.sub.2).sub.2 --NH.sub.2), --SH or ##STR2## or the grouping --NH--(CH.sub.2).sub.2 --NH--(CH.sub.2).sub.2 --NH.sub.2
X represents a moiety from the group --OCH.sub.3, --OC.sub.2 H.sub.5 and --OC.sub.3 H.sub.7,
Z represents the moiety --O--(CH.sub.2 --CH.sub.2 O).sub.q --R', wherein one of the H-atoms can be substituted by a methyl-group q being able to assume values of 2 or 3 and R' representing an alkyl of 1 to 4 carbon atoms, and
m represents the numbers 0 or 1 or 2, n the numbers 1 or 2 or 3, and p the values 0 or 1, on the condition that m+p is equal to or less than 2.
These new silane esters, when used in polyurethane sealing compositions, attain within a short time after processing very high adhesion and elongation factors, which surprisingly can be twice as high as they are when known organosilane esters are used.
The new organosilane esters can be prepared in a manner known in itself by the transesterification of known organosilane esters with di- or tri-ethylene glycol ethers. The ethylene glycol ether is best used in an excess; it is also possible, however, to use equimolecular amounts. The transesterification is advantageously performed at elevated temperature, preferably at the boiling temperature of the reaction mixture, while the simple alcohol that forms is removed by distillation.
Adequate yields can be obtained in the transesterification performed for the preparation of the aminoalkylsilane esters of the invention without the use of transesterification catalysts. In the preparation of mercapto- and glycidyloxyalkylsilane esters of the invention, however, it is recommendable to add known transesterification catalysts, such as titanic acid esters, for example, in order to obtain sufficient yields of the products in accordance with the invention.
The transesterification product contains, in addition to a small amount of unreacted glycol ether, mostly the completely transesterified organosilane. Depending on how the reaction is conducted and how great an excess of glycol ethers is selected, however, partial organosilane esters of the glycol ethers are also formed. Basically, it is possible to separate these partial esters from the triesters of the glycol ethers by distillation, but for the applications cited, especially use in polyurethane sealing compositions, this separation is not necessary.
Suitable starting products for the preparation of the glycol esters of the invention are the corresponding organofunctional trialkoxysilanes, the alkoxy group being preferably a methoxy or ethoxy group. It is also possible to use the corresponding organochlorosilanes as starting products and esterify them directly with the glycol ethers by methods known in themselves. When using aminosilanes as starting material, one H-atom of the amino group can be substituted by an alkyl group with one or three c-atoms or by an aminoalkyl group, which can also be substituted in the same way. An example is: H.sub.2 N--(CH.sub.2).sub.2 --NH--(CH.sub.2).sub.2 --NH--(CH.sub.2).sub.3 --S.(OCH.sub.3).sub.3.
Glycol ethers which can be used in the preparation of the products of the invention are the di- and tri-ethylene or propylen glycol monoethyl ethers whose ether moieties have 1 to 4 carbon atoms. Examples of such glycol ethers are: diethylene glycol monomethyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol monoethyl ether, triethylene glycol mono-n-butyl ether, diethylene glykol monoethyl ether, isomers of dipropylene glykol mono ethyl ethers and dipropylene glykol mono-iso-propylether.
The organofunctional group of the new silane esters is preferably separated from the silicon atom by three CH.sub.2 groups. The number of the methylene groups can, however, be less if, for example, beta-aminoethyltrimethoxysilane is used as starting product.
The new compounds are used either by adding them to the polymers whose adhesivity is to be improved or by applying them to the surface that is to be treated with polymers. When they are used as additives, they are added to the polymers, the sealing compositions for example, in an amount of about 0.5 to 1.5% by weight. It is also possible, however, first to react the compounds with highly reactive organic compounds before adding them to the polymers, and then to use the reaction product as the additive.
The pretreatment of substrates with the compounds of the invention is performed either with the latter dissolved in organic solvents or in the form of aqueous hydrolyzates. The concentration of such solutions or hydrolyzates is not critical. An organosilane ester content between 1 and 5% by weight will generally be selected.
Surprisingly, the new organosilane esters can be used particularly well in the form of aqueous hydrolyzates, since such hydrolyzates are very stable. These hydrolyzates are also easy to prepare, since the compounds of the invention dissolve and undergo hydrolysis in water much more rapidly than the known organosilane esters. On the basis of these good hydrolysis properties, the present compounds can also be hydrolyzed perfectly well in aqueous salt solutions. Even hydrolyzates prepared with a 15% aqueous ammonium sulfate solution are stable for much longer than 14 days.
Substrates suitable for pretreatment with the compounds of the invention are a great number of inorganic-oxidic materials such as, for example, glass in its various forms of fabrication, ceramic, concrete, tiles or metals such as aluminum, magnesium, copper, or alloys containing these metals. Also mineral fillers, especially silicatic fillers, and inorganic pigments such as iron oxides, titanium oxide or zinc oxide, can be pretreated with the compounds of the invention.
The pretreatment of the substrates is performed for the purpose of improving the adhesion between the substrates and a variety of polymers. Fibers, fillers or pigments can be bound into polymers better than they can without the addition of these compounds. This improved action becomes apparent even if only 0.1 wt-% of the silanes of the invention is applied to the above-named substrates.